Acute inflammation is responsible for tissue damage in the upper reproductive tract during Chlamydia trachomatis infections. These inflammatory responses are mediated by mitogen activated protein kinases (MAPK) ERK and NF-kB signaling pathways. Here we propose a research plan to define the molecular mechanism underlying chlamydial manipulation of these pathways. Infection with C. trachomatis leads to a sustained, non-canonical activation of ERK. We hypothesize that activation of ERK during infection is mediated by secreted Chlamydia effectors. We screened a library of chlamydial proteins in the yeast Saccharomyces cerevisiae and identified four genes that activate the yeast cell wall integrity (CWI) pathway, a MAPK pathway that bears strong functional resemblance to the human ERK MAPK pathway. Two of these genes, ct621 and ct695, encode uncharacterized proteins that are secreted into the host cytosol during Chlamydia infection. We propose that these effectors interact with and activate the ERK pathway. I propose genetic and molecular approaches in S. cerevisiae to characterize CT621 and CT695 and define the molecular basis for their manipulation of MAPK signaling. Activation of NF-kB (p65/RelA)-mediated signaling is important for the initiation of innate and adaptive immune responses. While infection by several bacterial pathogens trigger NF-kB activation, infection by Chlamydia does not. Lack of detectable NF-kB activation is partially due to the activity of the chlamydial effectors ChlaDUB1 and CPAF. However, these effectors exert their activity in the latter stages of infection implying that an alternative mechanism of suppression is deployed early during infection. We screened a limited collection of plaque-purified, EMS-derived Chlamydia mutants and identified two independent mutants that tamper with NF-kB signaling in early stages of infection. We propose to characterize these mutants and broaden our screen with a more comprehensive collection of mutants to define all factors that modulate NF-kB signaling early in infection. By employing these novel forward genetic approaches we aim to delineate chlamydial strategies underlying the manipulation of host signaling pathways important in inflammation.